1. Field of the Invention
The mammalian immune system provides one of the major defense mechanisms against disease. It has also for a long time been the sole source of antibodies. These molecules are almost uniquely capable of binding to a specific structural element of an organic compound. By virtue of this ability antisera have found increasing use in diagnostics. The antisera prepared by immunizing an animal is a heterogeneous mixture with a broad range of binding ability. Where antigens are involved, having a plurality of determinant sites, the antiserum which forms will have antibodies binding to the various determinant sites. In addition, the antisera which are normally isolated from serum will have a major proportion of antibodies unrelated to the immunogen of interest.
The recent discovery of Kohler and Milstein, Nature (1975), 256, 495-497, led the way in preparing monoclonal antibodies. These antibodies are homogeneous compositions having uniform affinity for a binding site, although there can be some contamination of light or heavy chain from the fusion partner.
The Kohler and Milstein work was limited to mouse antibodies. Subsequently, in 1980, the ability to cross human cells to produce hybridomas capable of excreting human antibodies was reported by two different groups. Having shown that human antibodies can be produced by human hybridomas, many improvements in the ability to produce antibodies may now be forthcoming.
In producing antibodies from human hybridomas, there are many considerations. One consideration is the degree to which the fusion partner--the immortalized cell--produces light or heavy chains or other immunoglobulin different from the immunoglobulin of the immunized cell, so as to contaminate the monoclonal antibody composition. Another consideration is the efficiency with which the fusion may be performed. That is, the number of viable hybridomas which are produced per 10.sup.5 human lymphocytes employed in the fusion.
Additional considerations include the nature of the required nutrient medium. The nutrient medium is important for a number of reasons. First, fetal calf serum is in short supply and has become extremely expensive. Therefore, it presents a serious deterrent to commercial production of human monoclonal antibodies. Secondly, because of the spectrum of materials present in fetal calf serum, separation and purification of the human monoclonal antibodies is complicated.
Therefore, while human monoclonal antibodies can now be prepared to a wide variety of haptens and antigens, there will still need to be substantial improvements. These improvements will involve the fusion partners and the manner in which the human monoclonal antibodies are prepared, particularly where the use of the monoclonal antibodies are for therapeutic purposes.
2. Description of the Prior Art
Olsson and Kaplan, Proc. Nat'l. Acad. Sci. U.S.A. 77, 5429-5431 (1980), describe the establishment of a continuous culture of purely allogenic human hybridomas secreting specific human antibody having myeloma cells as the fusion partner. Nowinski et al., Science, 210, 537-539 (1980), describe the isolation of a mouse-human hybridoma secreting a human monoclonal antibody against Forssman antigen. Croce et al., Nature, 288, 488-489 (1980), describe the production of human antibodies from a hybridoma using as a fusion partner a HPRT-deficient human B-cell line. The fusion partner was crossed with peripheral lymphocytes and secreted human IgM specific for measles virus nucleocapsids. Royston et al., Manuscript in Press and patent application Ser. No. 247,652 disclose the isolation and use of a human B-lymphoblastoid cell line as a fusion partner, the cell line is referred to as UC 729.